Various types of displays such as a liquid crystal TV, a plasma display (PDP) and an organic EL display in addition to a CRT have been developed, and the size thereof has been made larger. In accordance with a larger image plane and a higher image quality, it is usual to paste up an optical film provided with such as an antireflection layer on the front surface of a display to improve the visual recognition. Further, such a display comprising a large image plane is liable to be damaged due to direct hand touch or object contact. Therefore, an antireflection film provided with a hard coat layer, in which a hard coat layer is generally formed on a support and such as an antireflection layer is formed thereon, has been utilized to prevent abrasion.
As an antireflection film, a wide film having a width of not less than 1 m and further not less than 1.4 m has been required particularly due to a larger image plane. However, in the case of such a wide film to realize a large size as described above, color unevenness and periodical unevenness may be generated with respect to such as antireflection ability, tinting degree, phase difference ability and visible angle enlargement ability, and optical film provided with higher uniformity has been required without a difference between the outside and inside of a optical film roll, a difference between the center and side edge portions in the width direction, and a difference by lots. Further, film without deformation of a roll is required with respect to handling in the production process.
Heretofore, in the case of handling long rolled plastic film, known is a method, in which such as winding cinch and creasing during storage of a wound roll are prevented by providing a portion thicker than the film plane, which is called as a knurling or an embossing, on the both side portions of film (for example, refer to patent literatures 1 and 2).
On the other hand, various optical film having various types of functional thin layers on a long rolled plastic film substrate have been known, and to perform a thermal treatment, called as curing or aging, is known to improve strength of the thin film or to obtain a certain strength in a short period after forming a functional thin layer on said substrate (for example, refer to patent literatures 3 and 4). In these disclosed methods, it is described that optical film having a high surface hardness can be prepared by a thermal treatment, as a rolled form after having been coated and dried, at 40-150° C. for from 30 minutes to a few weeks.
However, in these conventional technologies, it is difficult to prepare optical film having a high uniformity without generation of color unevenness by applying these technologies to production of optical film particularly having a wide width, and strongly demanded has been a production method of high uniform optical film without generation of roll deformation and color unevenness as well as provided with a small difference by lots and a small difference between the outside and center of a roll.
Further, a thermal treatment in a wound and rolled state may be provided with respect to a substrate of rolled film having a coated layer. For example, there is a method to improve physical properties of a coated layer or film itself by a thermal treatment of a re-wound rolled film after such as a hard coat layer and an antireflection layer have been provided on a substrate of rolled film. However, it has been proved that there is a problem of significant increase of curl by a thermal treatment of a film substrate having a coated layer in a wound state as a roll form.
[Patent literature 1] JP-A No. 2002-211803 (Hereinafter, JP-A refers to Japanese Patent Publication Open to Public Inspection.)
[Patent literature 2] Japanese Patent No. 3226190
[Patent literature 3] JP-A No. 2001-91705
[Patent literature 4] JP-A No. 2002-6104